This invention relates to a rear projection-type multi-display apparatus in which a plurality of rear projection-type multi-display devices are arranged in contiguous relation to one another to form a large screen, and more particularly to a rear projection-type multi-display apparatus in which the screen is curved in a three-dimensional manner.
Recently, a display system, used in a play apparatus in an amusement park, a training apparatus such as a drive simulator and a flight simulator and so on, has now been required to provide a simulation space which makes the viewer feel as if he were in the scene in the picture image so that the viewer can perceive the realism, thereby enhancing the quality of the play and the degree of the training. In such a display system, what is to be perceived by the viewer through the sense of sight, the sense of hearing and so on are given to the viewer through the picture image, sound, the sense of acceleration and etc. In this case, the perception effect by the picture image is the most effective though there is the difference from one viewer to another, and therefore the image with a wider angle of visibility gives the more appealing realism.
For achieving such an image with a wide visibility angle, there has existed a front projection-type, dome-shaped display device in which an image is projected from the viewer side onto a dome-shaped reflecting screen provided in overhanging relation to the viewer.
FIG. 30 is a schematic, vertical cross-sectional view of such a front projection-type, dome-shaped display device as disclosed in U.S. Pat. No. 5,433,670. In this Figure, an image projected from a front projection device (projector) 90 is reflected by a reflecting screen 91, and reaches the viewer seated on a viewer's seat 23. In the front projection device 90, an image, displayed on a projection-type CRT (cathode ray tube), a liquid crystal display (which serve as a small image-generating source) or a film, is magnified by a fisheye-type projection lens, and is projected on the dome-shaped reflecting screen 91. Although the front projection device 90 is located above the head of the viewer in the illustrated example, it can be located at one side of the viewer, at the foot of the viewer, or at any other suitable position.
As a simpler system which can provide an improved picture quality, and can easily provide a large screen, there have now been increasingly used display devices (e.g. a rear projection-type television) for business purposes, in which an image, displayed on a projection-type CRT or a liquid crystal display serving as a small image-generating source, is magnified by projection lenses, and is projected on a rear projection screen or transmission screen.
In such a rear projection-type display device, where a projection-type CRT has been used as the image-generating source, there has heretofore been used a system in which in order to make the brightness on the transmission screen sufficiently high and also to maintain the fineness of the image, the projection-type CRT and the projection lens have been used for each of three primary colors (red, green and blue), and these three color images are combined together on the rear projection screen. FIG. 31 is a transverse cross-sectional view showing an optical system of an ordinary rear projection-type display device. As shown in this Figure, an image on each projection-type CRT with a diagonal size of about 5 inch is magnified 8.about.12 times by a projection lens 60. The three projection-type CRTs 61 to 63 are arranged or juxtaposed in an inline fashion in such a manner that the G CRT 61 is disposed between the left-side B CRT 63 and the right-side R CRT 62. Image light rays are combined together on a rear projection screen 65. Each projection-type CRT and the associated projection lens are connected together by a bracket 66.
FIG. 32 is a perspective view of an important portion of a conventional rear projection screen used in such a rear projection-type display device. As shown in this Figure, the conventional transmission screen consists of two sheets, that is, a Fresnel lens sheet 50 and a lenticular lens sheet 70. A light-incident surface 52 of the Fresnel lens sheet 50 is planar or flat while a Fresnel convex lens is formed on its light-outgoing surface 53. The Fresnel convex lens on the light-outgoing surface 53 of the Fresnel lens sheet 50 functions to convert the image light flux, incident on the light-incident surface 52, into generally parallel rays of light emerging from the light-outgoing surface 53, so that this Fresnel convex lens serves to make the brightness of the transmission screen uniform over the entire area thereof.
FIG. 33 is a transverse cross-sectional view of an important portion of the lenticular lens sheet 70. As shown in FIG. 32 and 33, the lenticular lens sheet 70 has a plurality of elongate lenticular lenses formed on its light-incident surface 71, and these elongate lenticular lenses extend in a vertical direction of the screen surface, and are juxtaposed in a consecutive manner in a horizontal direction of the screen surface. Elongate lenticular lenses and light-absorbing stripe portions 73 of a predetermined width are alternately formed on a light-outgoing surface 72 of the lenticular lens sheet 70 in a consecutive manner, these elongate lenticular lenses and these light-absorbing stripe portions extending in the vertical direction of the screen surface. Each of the lenticular lenses on the light-incident surface 71 has a generally semi-oval, transverse cross-sectional shape, and the configuration and characteristics thereof are described in detail in Japanese Patent Unexamined Publication No. 58-59436.
When viewing an image on a display device in a bright room, light in this room, which serves as external light, is reflected by a screen, and this light is seen as superposed on image light, so that the displayed image is often clearly invisible. The above-mentioned lenticular lens sheet serves to reduce the reflection of the external light in the display device.
Incident light 74, refracted by the vertically-elongate lenticular lens, is converged into a region of a predetermined width on the light-outgoing surface 72, as shown in FIG. 33. Those portions of the light-outgoing surface 72 from which the light will not go out are coated with black paint or coating to provide the light-absorbing stripes 73. By doing so, the reflection of the external light on the screen can be greatly reduced. If the area ratio of light-absorbing stripes to an overall light-outgoing surface of a conventional lenticular lens sheet is about 50%, the reflection of external light at the light-absorbing stripes is very small, and therefore can be regarded as being substantially zero, and the average reflectance of the external light at the screen surface is reduced about 50% as compared with the case where no light-absorbing stripe is provided. Therefore, if external light of the same intensity is present, the reflection intensity is reduced to a half level.
In connection with this rear projection-type display device, in order to obtain a more appealing realism, there has been proposed a rear projection-type multi-screen display apparatus in which a plurality of rear projection-type display devices are combined together vertically and horizontally so as to display a large picture image. With such a multi-screen system, a large screen, for example, with a diagonal size of 200 inch can be relatively easily provided while keeping the diagonal size of each individual rear projection-type display device to about 40 inch, and therefore the magnification of the image of the CRT by the projection lens needs only to be about 8 times, and this is advantageous from the viewpoint of brightness and fineness.
However, when it is desired to provide a picture image which gives such a realism to the viewer that he feels as if he were in the scene in the picture image, a satisfactory effect can not be achieved if the screen surface is flat or planar even though the screen has a large size, and it is necessary to provide the type of display apparatus in which the screen is disposed in generally surrounding relation to the viewer.
Therefore, in the conventional rear projection-type multi-screen display apparatus, there has been used a technique in which the individual screens are combined together in such a manner that they are inclined at an angle with respect to each other in the horizontal direction, thereby curving the overall screen in the horizontal direction.
FIG. 34 is a perspective view of one conventional rear projection-type multi-screen display apparatus having a horizontally-curved screen. In this rear projection-type multi-screen display apparatus shown in FIG. 34, rear projection-type display devices are arranged in three rows and four columns in contiguous relation to one another. Any two horizontally-adjacent rear projection-type display devices are connected together at an angle of 30 degrees in the horizontal direction. The ratio of the width to height of a transmission screen of each of the rear projection-type display devices is 4:3, and this screen has a diagonal size of 40 inch. In FIG. 34, reference numeral 3 denotes a unit support frame supporting the rear projection-type display unit containing a projection device (projector) 4, and a rectangular screen (transmission screen) 1 is supported on a screen support frame 2 mounted on a front side of the unit support frame 3. Reference numeral 8 denotes a support base on which the multi-screen display apparatus is supported.
FIG. 35 is a horizontal cross-sectional view of the rear projection-type multi-screen display apparatus shown in FIG. 34. As shown in this Figure, when the viewer 9 is spaced 1.5 m from the screen, the angle of visibility in the horizontal direction is about 120.degree., so that the enhanced realism can be obtained in the horizontal direction.
The above-mentioned front projection-type, dome-shaped display device of FIG. 30 could not provide a picture image, giving the enhanced realism, mainly for reasons mentioned below.
A first problem is that since the projection device is located at that side of the screen where the viewer is present, the projection device comes into the sight of the viewer while the viewer watches the picture image, so that he felt not fully absorbed in the picture image. Besides, when the diameter of the dome is not more than 4 m, it has been difficult for the viewer to take an appropriate viewing position because of interference with the projection device.
A second problem is that since it is necessary to cover a wide area by the single projection device, the magnification of the image by the projection lens need to be high, so that a relatively dark image could be provided. If the screen size of the image source is, for example, 5 inch in diagonal size, the magnification need to be 24 times for projecting an image on a screen with a diagonal size of 120 inch, and its brightness is about 1/600 of that of the image source. Although the brightness can be enhanced by increasing the number of projection devices, this invites problems that the space for installation of the projection devices increases, and that a large space is required.
A third problem is that when the magnification of the image by the projection lens is high, the fineness of the picture image is sacrificed.
On the other hand, the conventional rear projection-type multi-screen display apparatus does not suffer from the brightness and fineness problems which the front projection-type, dome-shaped display device encounters. Furthermore, in the case of the rear projection-type display device, the projection device is located on the side of the screen remote from the viewer, and therefore even if the number of projection devices is increased, no limitation is presented to the viewing position, and the projection devices will not come into sight. Therefore, the multi-screen system can be easily formed by increasing the number of projection devices. For example, let's assume that the rear projection-type display devices each having a diagonal size of 40 inch are used, a required magnification of a 5-inch screen of a projection-type CRT into a diagonal size of 40 inch is relative small, that is, 8 times, and accordingly, the brightness becomes 1/64. Thus, each individual rear projection-type display device can achieve sufficient brightness and fineness.
In the conventional rear projection-type multi-screen display apparatus, however, although the screen can be curved in either the horizontal direction or the vertical direction to widen the visibility angle, it has been impossible to curve the screen in both directions so as to widen the visibility angle in both the horizontal and vertical directions.
For example, in the rear projection-type multi-screen display apparatus shown in FIGS. 34 and 35, a sufficient visibility angle in the vertical (upward-downward) direction can not be obtained.
FIG. 36 is a vertical cross-sectional view of the above conventional rear projection-type multi-screen apparatus. When the viewer 9 is spaced 1.5 m from the screen surface, and watches the screen as shown in FIG. 36, the visibility angle in the upward direction is about 45.degree.. However, the angle of viewing of the upper edge of the screen by the viewer with respect to a direction 80 normal to the screen is 45.degree., and the distortion of the image viewed by the viewer increases, so that the substantial visibility angle in the upward direction is further reduced.
The rear projection-type display device weighs 50.about.100 kg, and therefore when the number of these display devices to be stacked increases, they could not be assembled together easily.
Another problem with the rear projection-type display device is color shift which means that the color varies depending on the viewing angle. In the system using three projection lenses, red (R) image light, green (G) image light and blue (B) image light are incident on the transmission screen at respective different angles, and therefore there exit different viewing angles respectively at which the three (R, G and B) outgoing image light beams have increased intensities. This color change depending on the change of the viewing angle is called "color shift". In the rear projection-type display device employing the conventional CRTs as shown in FIG. 31, the R projection lens and the B projection lens face the transmission screen at respective angles of about .+-.10.degree.. This angle is called "converging angle". The difference between the viewing angles which make the respective color (R, G and B) image light beams (which go out from the transmission screen) most intense, respectively, is corrected by the transmission screen, and therefore these angles are reduced to about a half of the converging angles. However, there still exists the difference of about .+-.5.degree. between the viewing angles which make the respective three color (R, G and B) image light beams the most intense, respectively. Therefore, when the screen is assembled in a curved manner, the color balance is lowered particularly at the joint portions of the screen, and in some cases the screen is not suited for practical use.
FIG. 37 is an enlarged, schematic, horizontal cross-sectional view of the joint portion of the screen in the conventional rear projection-type multi-screen display apparatus. In this Figure, the rectangular screens 1 are combined together to provide the overall screen 65 in such a manner that any two of the horizontally-adjacent rectangular screens 1 are connected at an angle of 30.degree. with respect to each other. At the joint portion of the screen 65, viewing angles 81 of the viewer 9 with respect to directions 80 normal respectively to the left and right screens 1 are different in .+-.15.degree. between the left and right screens 1 as shown in FIG. 37, and therefore a change in the viewing angle causes a change in the color, so that the color balance between the right and left screens is deteriorated.
Furthermore, when the screen is curved, the image light beam is incident upon the screen from that screen generally facing it, so that the contrast of the picture image is affected.
FIG. 38 is a schematic, vertical cross-sectional view of one example of a rear projection-type multi-screen display apparatus having a curved screen. When the screen is curved as shown in FIG. 38, image light going out from one screen surface is reflected by another screen surface, and this reflection light 82 is directed toward the viewer 9, so that the contrast of the picture image is degraded.
U.S. Pat. No. 5,137,450 discloses a rear projection-type multi-display apparatus comprising a plurality of relatively large screens for covering the sight of the viewer. U.S. Pat. No. 5,179,440 discloses a rear projection-type, dome-shaped multi-display apparatus in which a peripheral wall and a ceiling are covered with a plurality of relatively large screens. U.S. Pat. No. 5,253,049 discloses a rear projection-type, tunnel-shaped multi-display apparatus in which side walls of a passage as well as a ceiling are covered with large screens. However, the rear projection-type multi-display apparatuses disclosed in these U.S. patents has a drawback that light, passing through one screen, is incident as external light on another screen, thereby degrading the picture quality.